1. Field of the Invention
This invention relates to an adapter for a self-programming printed circuit board tester.
2. Description of the Prior Art
Printed circuit board testers with which unassembled (i.e. prior to component insertion) printed circuit boards are inspected for insulation failures and contact faults between the separate conductor paths are known per se. With these instruments, an adapter is set up on a printed circuit board so that its contact pins are positioned on corresponding test points of the printed circuit board. An example of such an adapter is described in Luther, U.S. Pat. No. 3,996,516. These contact pins are connected with corresponding contacts of a connecting plug to which the tester itself is connected. During testing, the instrument determines with what other test points each individual test point is conductively connected. The results obtained are compared with reference or design results that correspond to results obtained from a faultless printed circuit board. If, for example, an extra contact is found, this indicates an insulation failure. If, on the other hand, the instrument detects a conductive connection less than the reference or design result, this signifies that a contact fault, such as a break in conducting path, exists.
"Automatic programming" printed circuit board testers have recently been developed. In these testers an adapter is set up on a fault-free master printed circuit board. By means of a suitable program the tester undergoes a learning cycle during which it interrogates separate contact pins of the adapter to ascertain whether a conductive connection exists with any other contact pins of the adapter. The results of each interrogation are stored in a memory of the printed circuit board tester and are retrieved for comparison purposes during the actual testing process. Thus, the electronics of the printed circuit board tester learns from the master board which points of such master board are insulated and between which test points conductive connections exist. Use of the tester for testing a given type of printed circuit board therefore begins with the learning of the testing program from a master board.
If the tester is to be used to test another type of printed circuit board which has a different conductor path layout, the electronics of the tester must learn a new testing program from a corresponding new master board on which a corresponding new adapter is set up. In the process, the testing program used for the type of board previously tested is erased and lost.
If later the tester is once again used for testing the first type of printed circuit board, the first testing program must be learned all over again, with the corresponding adapter again being set up on a master board and the learning program again run off. Here the following problems may occur:
If an adapter has for example lain on a shelf for some time and one of its test pins has become defective, for example by breaking off or by oxidizing or if the defect is not detected, when the adapter is set up on a master board considered to be good, the tester electronics will learn a defective program. In addition, the original master board originally used, which likewise had to be stored, may itself have sustained damage. If a new printed circuit board considered good is used as a master instead of the original master board, it may contain an undetected manufacturing defect. It is also possible that the connection of the adapter to the printed circuit board tester may be defective, so that this, too, may lead to a faulty testing program. The use of a faulty program, however, leads to faulty boards being found to be good and fault-free boards being erroneously found to be defective.